Dokku is a lightweight PaaS solution that let's you essentially have a mini self-hosted Heroku. This means you can easily take a web application (Django, Rails, etc.) and deploy it with little to no setup. While Heroku offers scalability and support, it does so at a significant cost ($) beyond a very low volume; if you're planning to deploy lots of small or in-development apps, then you don't necessarily need everything Heroku offers, you just need an easy way to (git) push your apps out there.